a Linkshell mate uses Scoreboard too and does not have this problem, his records 100% of the time, Idle or Engaged. i even downloaded a new Battlemod.
It has nothing to do with Battlemod.
Windower exposes a field we can query to indicate "in combat." I made Scoreboard only accumulate damage/dps/etc whenever this is true, in an attempt to keep it from doing too much busy work during downtime, as well as to try to maintain a more accurate estimation of true DPS. In the simplest terms, Windower's "in combat" query is true whenever you have battle music playing or you're engaged. The former is unfortunately affected by the /battlebgm toggle.
When I initially wrote and tested this mechanic, it was fine for all people as far as I know. ie, just provoking would cause one to be considered in combat and if anyone in your alliance was in combat, you would also be in combat. But something changed. I've gotten varied reports from people about it no longer working or working inconsistently.
So like I mentioned before, some ideas were tossed around about how to make this "in combat" query more accurate and indeed Mafai pushed out this change, but the issue seems to still be there. This probably means I should solve it on the Scoreboard side, since there actually isn't any clean solution that could be done at the core Windower level.
Anyways, thanks for your patience with this. I was hoping Mafai's fix would have sorted this out for folks but I'll consider what I can do on my end.